extract_utils: Fix doubled path separator

* $DST_FILE is already prefixed with "/", don't double it.

Change-Id: I2655313abd7720a54b20f541a95960ae9ec373ad

build/tools/extract_utils.sh

@@ -1533,8 +1533,8 @@ function extract() {
         fi
 
         # Strip the file path in the vendor repo of "system", if present
-        local VENDOR_REPO_FILE="$OUTPUT_DIR/${DST_FILE#/system}"
         local BLOB_DISPLAY_NAME="${DST_FILE#/system/}"
+        local VENDOR_REPO_FILE="$OUTPUT_DIR/${BLOB_DISPLAY_NAME}"
         mkdir -p $(dirname "${VENDOR_REPO_FILE}")
 
         # Check pinned files